The process in forming deeply drawn containers requires a lubricated sheet stock for proper forming. Such lubricants include peanut oil, lanolin, petrolatum and castor oil, and many others. It is possible to deeply draw a container lubricated with any of the mentioned lubricants and others, see for example U.S. Pat. No. 4,042,515. Deep drawing permits forming a two-piece drawn can which is a preferred container in that the only seam is at the cover. The practice of heavily lubricating the sheet stock for a two-piece deeply drawn can is necessary because of the stresses introduced during forming. While certain chlorinated paraffins when used as draw lubricants may be post coated without removal they are not approved for such use in a food container by the Food and Drug Administration without complete removal prior to post coating. The lubricant of the present invention is approved when applied as set forth and post baked. No other acceptable technique is available to manufacture drawn and redrawn cans which will permit direct post coating operations on the completed cans (on either the inside or the outside surface). The most frequent method of coating application is by post spraying the cans using a typical can makers spray machine, where the cans are brought into position in front of a stationary spray nozzle, are sprayed, and are then carried away to a curing oven. Prior to that operation, all cans to be sprayed must be washed thoroughly to remove all traces of lubricant used to allow forming of the original plate into a container shape. This applies to cans made by draw/redraw methods or by drawing and ironing techniques (see for example U.S. Pat. No. RE 27,662). The problem in both cases with the cleaning operation is that the lubricant has been forced into all available pores, aberrations, interstices, etc. in the metal surface due to the high pressure applied by the tooling to the metal in order to form it, in the presence of lubricant. The washing must be done with the aid of chemical cleaners, the cans must be rinsed with deionized water to remove all traces of the cleaner, and the cans must then be oven dried in order to eliminate spotting from residual rinse water. The cost of this operation depends to some extent on the size of the can, the number of cans produced per year, and other factors (such as neutralization needed in order to send the cleaning solution into a sanitary sewer system, quality of the water available for the original wash cycle etc.). Drawn containers of precoated metals are commercial but it is recognized that a post sprayed container can have superior product resistance for certain hard to hold foods.
The three-piece container has a body rolled into a cylinder which comprises a side seam and two double seamed ends. Such containers are normally precoated, do not require the use of lubricant during forming and, thus, are easier to process. In contrast, the need to remove the heavy lubrication on two-piece cans after deep drawing requires can washing and drying energy, equipment and materials. Each requirement is costly in terms of capital investment, plant space and energy consumption. In addition, the drying process is environmentally deleterious since vapors are driven off, fuel is consumed generating heat and products of combustion.
It is an object of this invention to eliminate the need to wash lubricants for deep drawing.
A further object is to provide a lubricant which will also effectively permit metal strip to be deeply drawn without surface damage to the metal from which the container is formed.
It is a further object to provide a lubricant which can be successfully overcoated during a post spraying operation and which will permit the post coating to form a strong bond with the container.